1. Field of the Invention
The present invention relates to an image forming apparatus such as a laser beam printer and, in particular, to a fixing unit of the image forming apparatus, a roller replacement auxiliary tool of the fixing unit, and a roller replacement method.
2. Description of the Related Art
A known fixing unit of an image forming apparatus such as a laser beam printer and a copier fixes a toner image on a recording medium by heating and pressing the recording medium maintaining the toner image on its front surface while conveying the same so as to be held between a heating roller and a pressure roller.
Inside the heating roller, plural lamps are provided as heat sources. Generally, image forming apparatuses whose print speed is fast and that are adapted to store high ream weight recording media require high heat capacity for fixing a toner image and thus have to maintain the heating roller at a certain temperature or higher, which in turn requires a higher fixing temperature.
When a maintenance technician replaces the heating roller because the heating roller maintained at high temperature comes to the end of its service life, he or she stops the operations of the image forming apparatus, extracts the heating roller from the fixing unit after causing the heating roller itself to be cooled to a certain level enough to perform a replacement operation, and replaces the heating roller with a new one. In this case, however, it takes time to cool the heating roller and greatly reduces an operating efficiency. In addition, this causes not only the degradation of the operating efficiency because the image forming apparatus is stopped for a long time, but also a large cost for replacement maintenance operations.
Recently, there has been demanded for the image forming apparatuses adapted to high print speed, high image quality, and various sheets. Furthermore, it has been requested that the fixing unit use some types of heating rollers such as one that has a thin PFA resin or the like coated on its front surface for the purpose of promptly supplying heat required for fixing a toner image when high print speed is demanded, one that has a silicon rubber or the like coated on its front surface for the purpose of minimizing the damage and bleeding of a toner image at fixation when high image quality is demanded, and one that has a PFA resin or the like coated on a silicon rubber layer when image quality having a certain degree and roller durability are demanded.
In order to respond to such a demand in the image forming apparatus, the heating roller must be changed correspondingly. Although there is some difference depending on the types, the heating roller has basically a high heat capacity and takes a long time to cool so as to be replaceable from a high temperature state at which the heating roller is maintained to supply the heat required for optimum toner fixation. The replacement of the heating roller is discussed in, for example, Patent Document 1 (Japanese Patent Application National Laid-Open Publication No. 5-504633).
FIGS. 1 and 2 are a partial cross-sectional view of the fixing unit described in Patent Document 1 and a perspective view of the fixing unit showing the heating roller being replaced.
FIG. 1 is the partial cross-sectional view of the fixing unit described in Patent Document 1. As shown in FIG. 1, one end of the heating roller 100 is supported by a frame 102 through a support flange 101. The support flange 101 has a bearing 103, and the bearing 103 is fitted in the opening end of the heating roller 100 together with a centering member 104. Although not shown in FIG. 1, the other end of the heating roller 100 is also supported by a support flange through a bearing.
The support flange 101 is fixed to the frame 102 through a wing screw 106. The support flange 101 is fixed to a holding claw 108 through a wing screw 107, and the holding claw 108 is used for setting the position of the heating roller 100 when the heating roller 100 is replaced.
Inside the heating roller 100, plural radiator modules 105 are arranged. First ends of the plural radiator modules 105 are held at the center of the support flange 101 through the holding member 109. Although not shown in FIG. 1, the other ends of the plural radiator modules 105 are also indirectly supported by the support flange through a holding member.
As shown in FIG. 1, a connector 110 provided at the ends of the plural radiator modules 105 is projected outward more than the support flange 101 where the plural radiator modules 105 are held at the center of the support flange 101. The support flange 101 is integrally provided with a grip 111 for replacing the heating roller 100. The grip 111 is provided so as to straddle the connector 110 of the plural radiator modules 105 projected from the support flange 101.
As shown in FIG. 2, when the heating roller 100 is replaced, an operator unfastens the wing screw 106 and extracts the heating roller 100 from the frame 102 together with the support flange 101 or the like by holding the grip 111 with one hand.
Generally, the heating roller for use in the fixing unit of this type is a cylinder having a diameter of about 100 mm and a length of 500 mm or larger, which is very heavy in weight. Under such a circumstance, when an operator extracts the heating roller 100 from the frame 102 together with the support flange 101 or the like by holding the grip 111 with one hand, an extracting operation is likely to be unstable due to the weight and heat of the heating roller 100 or the like. Therefore, during the replacement of the heating roller 100, there is a likelihood of causing the heating roller 100 to be brought into contact with other components such as the frame 102 to damage the front surface of the heating roller 100.
As described above, since the posture of the heating roller 100 becomes unstable and no auxiliary tool is provided for stabilizing the posture of the heating roller 100, an operator puts one hand on the heating roller 100 when replacing the heating roller 100 in an embodiment disclosed in Patent Document 1. However, when an operator touches the heating roller 100 at high temperature, he or she gets burned or gets soiled by a toner releasing agent and lubricant oil attached on the heating roller 100, which results in problems in operations.
In addition, since the grip 111 is integrated with the support flange 101 holding the plural radiator modules 105 and arranged near the ends of the plural radiator modules 105, the grip 111 itself is also at high temperature. Therefore, it is difficult for an operator to hold the grip 111 when replacing the heating roller 100.
Also, the grip 111 is used for rotating and holding the heating roller 100 when the image forming apparatus is in an operating state, and it is screwed to a link member (not shown). Therefore, the link member and screws are also at high temperature. For this reason, the separation of the heating roller 100 from the link member is an operation for handling members including the screws at high temperature, which results in problems in workability and safety.
Moreover, the grip 111 is provided at the center of the support flange 101, which in turn interferes with the replacement of the plural radiator modules 105. Therefore, the plural radiator modules 105 are restricted to be inserted in and extracted from the other support flange where the grip 111 is not provided, which results in problems in operations.
Furthermore, the grip 111 projects from the support flange 101. Therefore, space is wasted, which results in problems in the miniaturization of the image forming apparatus.
Furthermore, when an operator extracts the heating roller 100 from the frame 102 together with the support flange 101 or the like by holding the grip 111 with one hand, there is a likelihood of causing the heating roller 100 to be brought into contact with the frame 102 to damage the front surface of the roller. Therefore, the vicinity of the opening of the frame 102 is coated with felt 130 so as to be protected. However, when the heating roller 100 having a releasing agent and lubricant oil attached on its front surface is slid, a stain accumulates on the felt 130. Therefore, the above configuration is insufficient for protecting the front surface of the heating roller 100.
Furthermore, the felt 130 is required to be attached and separated every time the heating roller 100 is replaced, which results in complicated replacement operations. Moreover, the felt 130 is stained every time the heating roller 100 is replaced, which in turn requires the disposal of the stained felt 130 and the preparation of new felt 130.    Patent Document 1: Japanese Patent Application National Laid-Open Publication No. 5-504633    Patent Document 2: Japanese Laid-open Patent Publication No. 6-011984